Resonant Ultrasound Spectroscopy (RUS) describes the application of acoustic waves to mechanical structures in order to detect small defects. The frequencies of the acoustic waves are varied across the frequency range of interest by defining a response time interval, dependent upon the elastic properties of the material, and a frequency step interval, wherein the acoustic wave frequency is varied at intervals across a range of interest and measured over a predetermined response time interval. The structure vibrates when the drive matches the frequency of one of its characteristic modes. Higher order modes are targeted so that very small defects can be detected.
Referring to FIG. 1, performing RUS involves generating a signal with a signal generator 14, emitting the acoustic wave signal onto an object or part 12 with a drive transducer 16, detecting the vibration of the object with at least one receiving transducer 18, processing the output signal with amplifier 22, and analyzing the signal with computer 24.
The object is supported typically by three piezoelectric transducers, one for emitting the acoustic wave signal and at least one of the other two transducers for measuring the response. Obtaining reliable resonant data over a range of frequencies requires reliable part placement on the test station, as well as temperature compensation and sophisticated data analysis. In order to achieve reliability, the testing apparatus must be configured for each specific part. This includes a custom arrangement of the piezoelectric transducers as well as support pins or other structures for holding a particular part in place. The arrangement of positioning posts and piezoelectric transducers must be maintained at a predetermined spacing in order to provide accurate results. When the apparatus is reconfigured for a different part, the transducers and positioning posts must be relocated and fastened in place.
Reconfiguring the apparatus for different parts can be time-consuming and is particularly costly for industries where the number of each type of part is relatively low. For this reason, there is a need for a method and apparatus for conducting resonant inspection that reduces the costs associated with reconfiguration of the piezoelectric transducer and/or positioning post arrangement.